What are impermissible mixed metaphors?

Definition

Impermissible mixed metaphors are metaphors that conflict because they serve different purposes.

Examples (English)

The argument-as-journey and argument-as-container metaphors serve different purposes. Argument-as-journey can address the “direction” of the argument and the argument-as-container can address the “amount of content” of the argument. The incompatibility of the ideas of “direction” and “amount” in the same sentence makes the following examples semantically impermissible: